Success! Mostly...

I am not much of a craftsman and get a little trigger happy with electric tools... here was my process:

Used wireless dremel with the skinny drill bit cutting/engraving attachment and just went to town clearing out all the excess plastic below the TSS. From there used some files I had to make it as flush and cohesive as possible. Next used flat black touch up paint to paint over all sanded sections to match the color of the grill.

Up close and personal, you can see spots where I got a bit wayward with the dremel. But far and away it was a massive success. Can confirm nothing behind it and tss is snug as a bug. Really no clue why this plastic was there in the first place.

Light bar installed in a few days will post another pic.